This invention pertains to systems and methods for detecting pulses within electrical signals and, in particular, within surface electrocardiograms.
Implanted pacemakers generate pacing pulses in order to stimulate the heart to beat in the absence of spontaneous beats. Such devices, which may be either dedicated pacemakers or other devices with a pacing functionality (e.g., implantable cardioverter/defibrillators), thus produce detectable electrical signals when the heart is paced. Signals from implanted pacemakers often couple to the body surface and hence are present in electrocardiograms (ECGs). Pacing pulses in electrocardiograms are detected for two purposes: one, to provide the clinician with a marker showing pacemaker activity and, two, so that the visible pacemaker artifacts can be removed from the ECG waveforms. Prior designs for doing this involve filtering the incoming ECG data to a specific high frequency band (1-15 KHz) and then comparing the energy in the band to a threshold level. Refinements to this idea include variable sensing thresholds to help reject noise, and higher frequency filtering to attempt edge detection. Edge detection by high frequency filtering, however, is extremely susceptible to broadband noise from both telemetry and minute ventilation signals.
It is a primary object of the present invention to provide a system and method for detecting pacing pulses within ECG data. Pacing pulses have significant high-frequency energy due to the sharp transitions at the rising and falling edges of the pulse. A pacing pulse also has a significant amount of low-frequency energy that occurs in a particular time relation to the occurrence of the high-frequency energy. In accordance with the invention, an ECG signal is processed to determine its energy content in both high and low frequency bands. If such energy is present above a threshold amount in each band, and meets specified timing criteria, a pacing pulse is detected.
A system for detecting pacing pulses within an ECG input signal in accordance with the invention includes high-frequency and low-frequency bandpass filters for filtering the input signal into high-frequency and low-frequency components that represent the energy of the input signal within the respective frequency bands. Exemplary high and low-frequency bandpass filters would have center frequencies of approximately 1 KHz and 30 KHz. The system also includes pulse detection circuitry for detecting high-frequency and low-frequency energy pulses within the high and low-frequency components, respectively, and at least one timer for measuring one or more time intervals between detections of energy pulses. Logic circuitry is provided for detecting a pacing pulse within the input signal if the detections of the high and low-frequency energy pulses meet specified timing criteria. The timing criteria may then dictate that a pacing pulse is detected only if detection of a low-frequency energy pulse occurs within a specified time interval with respect to detection of a high-frequency energy pulse. In one embodiment, the logic circuitry detects possible rising and falling edges of a pacing pulse when first and second high-frequency energy pulses are detected by the pulse detection circuitry. The timing criteria for detection of a pacing pulse may then include detection of the second high-frequency energy pulse within a specified minimum time interval from the detection of the first high-frequency energy pulse. The timing criteria may further include detection of the second high-frequency energy pulse within a specified maximum time interval from detection of the first high-frequency energy pulse.
In order to distinguish sensed energy pulses from noise, the pulse detection circuitry detects energy pulses by comparing sensed energy pulses to a threshold value. In one embodiment, the pulse detection circuitry detects energy pulses in the high-frequency band by comparing a sensed pulse to a threshold value derived from a sensed RMS level in the input signal. In this manner, a dynamic noise floor is established. In another embodiment, the pulse detection circuitry detects energy pulses in the high-frequency band by comparing a sensed pulse to a threshold value based upon a prior detection of a high-frequency energy pulse. The threshold value based upon a prior detection of a high-frequency energy pulse may then be updated by the logic circuitry when a pacing pulse is detected. Particular embodiments of the pulse detection circuitry may combine threshold testing such that energy pulses are detected only if a sensed pulse exceeds thresholds based upon a sensed RMS level, a prior pulse detection, and a fixed value.